The present invention relates generally to injection molding and more particularly to a gas assisted injection molding system having improved gas nozzles.
Known gas assisted injection molding systems generally comprise a mold having an inner surface defining a cavity. A gas nozzle is selectively extendable into the cavity. In operation, a short shot of resin is introduced into the cavity. After initial resin injection, the resin is permitted to partially cool. The nozzle is extended into the cavity, piercing the partially cooled resin wall. Then, high pressure gas is injected into the resin through the nozzle. The pressurized gas displaces the molded resin, thereby forming a gas channel. Because the resin adjacent the surface of the mold cools faster than the resin in the center of the cavity, the pressurized gas generally displaces material from the center of the gas channel or thicker portions of the resin, toward the mold surfaces. In this manner, hollow articles or articles having hollow portions, are molded. The pressure of the gas is either maintained or profiled during the cooling phase, typically approximately 20 to 50 seconds. After the article has cooled, the pressurized gas inside the article is vented through the gas nozzle, thereby relieving the high pressure in the article prior to removing the article from the mold. The gas nozzle is then retracted from the cavity.
After the article is removed from the mold, the mold is reclosed and a subsequent cycle is operated in a similar manner. In the known system, when the pressurized gas is vented through the gas nozzle, some of the resin may be carried by the gas into the gas nozzle, thereby partially or completely plugging the nozzle with resin. At that time, the operation of the injection molding system must be temporarily ceased in order to clean the gas nozzle.